February 2002

"Backflow" water line attacks warrant further study

Ann Daniels
Professional Development Program Manager
APWA Kansas City office

Following the September 11 attacks, water utility authorities in St. Petersburg, Florida, are keeping a closer watch on system-wide water pressure. Cleveland officials are weighing whether to add more chlorine to their water so larger amounts of the chemical will remain in the pipes for longer periods of time. In Portland, Oregon, alarms are now triggered by smaller drops in water pressure than in the past.

Water utility officials across the country are taking steps to prevent terrorists from reversing the flow of water into a home or business. Sounds difficult, but when you realize it can be accomplished with a vacuum cleaner or bicycle pumpâ€”and using the resulting "backflow" to push poisons into a local water distribution systemâ€”the threat becomes more realistic. Such an attack would use utility pipes for the opposite of their intended purpose: Instead of carrying water out of a tap, the pipes would spread toxins to nearby homes or businesses.

This topic has dominated discussions among water officials since the September 11 attacks. Although utilities have posted extra guards to patrol reservoirs and treatment plants, officials say the greatest threat to the nation's water supply may be from the pipes that carry the water, not facilities that store or purify it.

"There's no question that the distribution system is the most vulnerable spot we have," says John Sullivan, chief engineer for the Boston Water & Sewer Commission and president of the Association of Metropolitan Water Agencies (AMWA). "Our reservoirs are really well protected. Our water treatment plants can be surrounded by cops and guards. But if there's an intentional attempt to create a backflow, there's no way to totally prevent it."

The large capacities of most reservoirs, holding between three million and 30 million gallons of water, would dilute any poison so significantly that terrorists would have to release enormous quantities to do serious damage. The purification at the plant would destroy most of the poison. By contrast, a backflow attack could spread highly concentrated amounts of poison to a few thousand homes or businesses, making the toxin far more effective.

The only backflow incidents on record, so far, have been accidental. Dozens of gallons of firefighting foam backed up through the hoses of firefighters in Charlotte, North Carolina, four years ago, and made its way into the city's water system, prompting officials to order thousands of residents not to shower or drink tap water for several days. In 1998, workers at a United Technologies Corp. Sikorsky helicopter plant in Bridgeport, Connecticut, added chemicals to the facility's fire prevention system to guard against corrosion. Some of the chemicals backed into the town's water system, deluging area homes with contaminated water that residents were told not to drink or use for washing or bathing.

Neither of these cases caused serious injuries, but they have startled many water officials. Even before September 11, fears of an accidental backflow incident led to the creation of a group called the American Backflow Prevention Association (www.abpa.org), which works with lawmakers, water officials, and engineers across the country. The group publishes a newsletter and an educational comic book for children that features a character named Buster Backflow.

Experts have long feared that terrorists would try an intentional attack. Gay Porter DeNileon, a journalist who serves on the National Critical Infrastructure Protection Advisory Group (a water-industry organization), said in the May issue of the journal of the American Water Works Association (AWWA), "One sociopath who understands hydraulics and has access to a drum of toxic chemicals could inflict serious damage pretty quickly."

While utility officials say it is difficult to fully prevent a backflow incident, they are hopeful that they can limit the damage through early detection. The beginning of a backflow attack probably would be marked by a sudden drop in water pressure in a targeted neighborhood as terrorists stopped the flow of water into a home or business. The pressure then would climb as attackers reversed the flow of water and began using it to carry poison.

Utilities regularly monitor system-wide water pressure, because a sharp and unanticipated decreaseâ€”at times other than, say, halftime of the Super Bowl, when tens of millions of American toilets flushâ€”can indicate that a pipe has burst. Most utilities monitor pressure at water treatment plants and inside the underground pipes that carry the water to nearby homes and businesses; some use advanced telemetric sensors inside pipes.

Since the recent events, many utilities say they have increased the frequency of their checks. "A small dropoff would attract attention it wouldn't have even a short time ago," says Michelle Clements, a spokeswoman for Oregon's Portland Water District, which serves 190,000 customers.

Jeffrey Danneels, a specialist in infrastructure security at Sandia National Laboratory in New Mexico, says that water officials might have a hard time detecting a backflow attack originating in a single home or apartment building. "The smaller the pipe, the harder it would be to notice," he says.

Another way to protect the public is to increase the amounts of chlorine or other chemicals added to water so that more of the chemical will remain in the pipes, providing residential protection against some toxins, according to Tom Curtis, deputy director of AWWA, which represents 4,300 public and private water utilities.

Even before the September attacks, some utilities had begun replacing the chlorine in the systems with chloramines, a related substance made from the combination of chlorine and ammonia that is believed to linger in pipes longer. Increasing the chemicals has drawbacks, however. "You can only go so far before people begin to complain about the taste," says Curtis.

Water officials say the only sure way of preventing a backflow attack is installing valves to prevent water from flowing back into the pipes. Many homes have such valves on toilets and boilers. But virtually none have them on sinks, partly because water officials long assumed that the biggest threat they faced was natural, such as an earthquake, flood, or hurricane carrying debris into a reservoir or pipe. Water officials say retrofitting existing structures with the valves would be prohibitively expensive.

"We're used to natural incidents. We're ready for them," says Sullivan of the AMWA. "But we've never really looked at what could happen if someone really wanted to come and get us. And that's a hard adjustment to make."

While most of this information is probably not new to water utility operators, being reminded of the seriousness of simple methods of attack is never a waste of time. Remind your water operators to be diligent in monitoring their gauges. Sometimes the simplest suggestions can make the biggest difference.